This invention relates to the formation of an indicator element containing a high contrast silver halide imaging layers and metallic reflective layers for a timing device.
Indicator elements or timing elements allow devices such as ink jet print heads to be accurately positioned in space. In general, timing control elements are either rotatable about a central axis, i.e., timing disk, or are movable in a linear direction, i.e., timing rule. Light, projected by a transmitter, passes through the control element, and is intercepted by the receiver. The receiver, responsive to the light, converts the light into an electrical signal capable of controlling machinery and other servo-mechanical devices.
Timing control elements typically are encoded with a selected window pattern, i.e., they have an annular or linear array of windows which alternate in a transparent window, opaque window, transparent window, opaque window pattern. While the transparent window openings allow the transmitted light to pass through the timing disk or rule, the opaque windows prevent the light from passing through the timing disk or rule.
Timing disks as a rule are fixed to a rotating shaft by means of a hub. For linear systems, timing rules are arranged at right angles to a source of light and the associated receiver generates an electrical signal in response to the incoming light. This particular application is used, for example, to control the feeding action of machine tools.
As the timing disk rotates or the timing rule moves in a linear direction, light is directed at the selected window pattern. Because of the window pattern, the transmitted light can only pass through a transparent window. In response to the light, the receiver generates an electrical signal.
The electrical signals serve to establish a control surface for the measurement of rotational speed, acceleration and more accurate positioning of servomechanical elements, as for example a printing head, a robot arm or a tool carrier.
Timing control elements can be made of glass, metal or plastic, however, plastic and metal are typically used in mass production applications. They are produced, for example, in the case of angle indicators or encoding units, e.g. ink jet printers, out of transparent films.
Timing control elements are generally constructed of light-sensitive film. Coding of the film occurs when the film is exposed to light passed through a template means. The coding results in the production of an alternating pattern of transparent and opaque windows. Individual disks or rules are then cut out of the film material to generate timing disks or timing rules, respectively.
Known timing devices utilize an arrangement whereby the transmitter is placed on one side of the timing structure and the receiver is placed on the other side of the timing structure to capture the light as it passes through the disk. This arrangement has been known to cause a number of problems, including: a requirement for a complex electromechanical apparatus, increased mechanical stress caused by oscillating loads, a larger footprint size for the timing device, and dirt forming on the timing structure, thereby preventing light from passing efficiently through the structure.
U.S Pat. Nos. 5,508,088 and 5,672,865 describe a timing device that comprises a metallic layer and a silver halide layer. While the invention does provide a timing device of good quality, it none the less suffers from poor adhesion of the light sensitive silver halide layers to the metallic layer. Poor adhesion results in the light sensitive layers delaminating from the metallic layers during wet processing and during final use as a timing device. Further, it is well known that most metals negatively impact the quality and density uniformity of the disclosed light sensitive silver halide layers. Finally, direct application of silver halide imaging layers to a metal layer may result in a significant reduction in the reflective properties of the metal layer as the metal layer can undergo oxidation at the moisture bearing silver halide gelatin binder interface reducing the quality of the timing device.
It has been shown that application of primer materials to the surface of the metallic layers does not achieve sufficient adhesion between the light sensitive silver halide layers and the metal layers. Further, the application of primer materials tends to reduce the reflectivity of the metal reflective layer requiring higher power sources for timing devices.
U.S. Pat. No. 6,291,150 describes a photographic print materials that contains a foil layer to provide an opaque layer to prevent high density backside ink printed graphics from interfering with the front side image. Further, the foil layer provides an oxygen and moisture barrier for the light sensitive imaging layers which improves the speed performance of unexposed light sensitive layers and improved fade resistance of printed and processed images.
U.S. Pat. Nos. 4,695,532 and 4,689,359 describe a discharge treated polyester film support having coated directly thereon a subbing layer comprising a mixture of gelatin and an aqueous vinyl acrylate copolymer having a ratio of gelatin to polymer of between 5:95 to 40:60 and a dry coverage of between 0.11 and 0.55 g/m.sup.2. Although this subbing system has good adhesion before processing, it has been found that adhesion after contact with photographic developing solutions is severely degraded. U.S. Pat. No. 5,639,589 (Bauer et al) describes a coating to improve adhesion of light sensitive silver halide imaging layers to polyester film.
There remains a need for a highly reflective timing element that has improved adhesion between the imaging layers and the reflective substrate. Further, there is also a need to protect the metal layer from scratching and abrasion.
It is an object of the invention to prove a highly reflective timing element
It is another object to provide a high contrast between the transmissive areas and opaque areas of the timing device
It is a further object to provide improved adhesion between the imaging layers and the reflective base.
These and other objects of the invention are accomplished by a material to form an indicator element comprising a base material and at least one photosensitive silver halide layer, wherein said base material comprises at least one specular reflective layer between two polymer layers wherein said polymer layer between said at least one specular reflective layer and said silver halide layer is substantially transparent.
The invention provides improved adhesion between the imaging layers and the highly reflective substrate. Further the invention provides a protective surface for the delicate metal layer and provides a double sided timing device.